Well, this is interesting. Earlier, I brought up NBC's move of Leno to 10 PM, and speculated that it might have something to do with Prime Time getting smaller. I just finished lunch, and what do I see queued up in my news reader?

A terrible fall season at NBC is forcing the network to consider scaling back the number of hours it airs programming, Chief Executive Jeff Zucker told an investor conference Monday.

I still can't find the older link, but this is not the first thing I've seen on this. I think TV - like newspapers - is in the midst of a rather large sea change. Unlike the 1970's, you simply can't get "everyone" to show up at 9PM for a popular show; there are just too many niches that interest too many people available, both on cable channels and online. That obviously impacts the ad rates you can charge, and gets right to the heart of the broadcast TV business model.

I think the era of narrow-casting is hitting TV, and it's going to hurt the networks the same way that Craigslist and E-Bay have hurt newspapers.